Adhesive compositions made with condensed phase polymers and sheet materials coated therewith

ABSTRACT

The present invention relates to pressure-sensitive adhesive compositions comprising tackified elastomeric copolymers or block copolymers, e.g., based upon styrene/isoprene, having a novel condensed phase structure wherein polymer branches occur along the polymer backbone, either at a predetermined location or at random locations. The invention also provides sheet materials coated with the adhesive compositions. The polymers of the present invention are made by a method which comprises the step of reacting, under polymerization conditions, hydrocarbyl lithium initiator, at least one anionically polymerizable compound, and an organometallic-substituted styrene condensing agent. The reactants may be added simultaneously to produce a copolymer with polymer branch segments randomly located along the polymer backbone or sequentially to produce a copolymer with branches located at the same predetermined location along the polymer backbone. The resultant polymers may be further reacted with a linking agent to form multi-arm copolymers. The resultant elastomeric polymers are compatible with any of a wide variety of known tackifier resins and plasticizers to produce unique pressure-sensitive adhesive compositions.

TECHNICAL FIELD

This invention relates to adhesive compositions derived fromanionically-prepared copolymers containing organometallic-substitutedstyrene and to sheet materials coated therewith.

BACKGROUND ART

Pressure-Sensitive Adhesive Art

Normally tacky pressure-sensitive adhesive (hereinafter referred to bythe abbreviation "PSA") compositions suitable, for example, for use inadhesive tapes must have an art-recognized (1952 Fall Symposium,Division of Paint, Varnish and Plastics Chemistry, American ChemicalSociety) four-fold balance of adhesion, cohesion, stretchiness andelasticity. PSA coated tapes have been produced and sold for at least ahalf century.

The early PSA tapes relied upon natural rubber for the elastomeric baseand wood rosins as tackifiers to provide adhesive compositions with therequisite four-fold balance of properties. While tackified naturalrubber provided a PSA composition which was of commercial significance,improvements in such compositions were sought because of the expandedexpectation level of performance of PSA compositions. Various improvedPSA compositions were thus developed.

Ionic polymerization produced block copolymer elastomers such as linearAB and ABA block copolymers which were likely candidates for theelastomer base in the PSA compositions and many were incorporated intosuch compositions to produce adhesives having high performancecharacteristics. For example, Harlan (U.S. Pat. No. 3,239,478) producedPSA compositions based on ABA block copolymer, tackifier resin andextender oil, recognizing that improved tack and cohesive strength couldbe obtained despite a heavy loading of extender oil. Miller (U.S. Pat.No. 3,519,585) produced an improved PSA composition having high peelstrength, creep resistance and tack by blending AB and ABA blockcopolymers with a tackifier resin.

Other elastomer candidates for preparing PSA compositions include radialteleblock copolymers and multiarm star block copolymers. The variouspolymer structures described by the terms "branched", "radial" and"star" are not the same. "Branched" is a generic term indicating anonlinear structure which may contain various polymeric subunitsappended to various places on a main polymer chain or backbone. Suchstructures are typically complex in nature and may be derived by freeradical or cationic polymerization. The term "radial" generally refersto branched polymer structures obtained by linking individual polymericsegments to yield a mixture of polymers having four or fewer arms joinedcentrally. The term "star" describes the structure of a multiarm polymerwith copolymer arms which are joined together at a nucleus formed of alinking group which is virtually a point relative to the overall size ofthe remainder of the polymer structure. Non-terminating coupling agents,those in which the polymerizing anionic structure is retained, aregenerally preferred as linking agents for "star" structures.

While several references disclose preparing adhesive compositions or PSAcompositions employing radial teleblock copolymers and multiarm starblock copolymers, none have recognized that novel anionically-preparedcopolymers containing organometallic-substituted styrene may be used toprepare PSA compositions nor that such compositions exhibit unusual meltviscosity characteristics as well as excellent adhesive properties. Forexample, St. Clair (U.S. Pat. No. 4,444,953) describes asymmetric starblock polymer prepared by terminally linking together a mixture ofstyrene-isoprene AB block polymers and isoprene homopolymers. The meltviscosity of such asymmetric star polymers is generally significantlyhigher than their linear counterpart. Marrs et al (U.S. Pat. No.3,658,740) discloses the preparation of PSA compositions by combiningbranched block copolymers with linear block copolymers, tackifiers andorganic solvents. Marrs' PSA formulation requires a solvent as acritical element to provide an adhesive formulation which bonds to awide variety of substrates but fails to address the need for hot meltprocessability. Nash (U.S. Pat. No. 4,163,764) discloses the preparationof PSA compositions employing a two-step process in which amonovinyl-arene monomer, such as styrene, is first polymerized, followedby a second stage where diene monomer and additional initiator are addedand the resulting polymerized product linked to give linear orradially-branched polymers. These polymers, when formulated withtackifiers, exhibited superior tack and creep resistance. Feeney et al(U.S. Pat. No. 4,288,567) employs a branched block copolymer describedin Prudence (U.S. Pat. No. 3,949,020) and relies upon a solutionpreparation process to achieve an adhesive composition having increasedtack, faster molten solution time, and improved tack retention in hotmelt blends.

Copolymer Art

While several references disclose the preparation of various copolymerswhich may be suited for use as a rubbery base material for PSAcompositions, none known to applicants discloses theanionically-prepared copolymers containing organometallic-substitutedstyrene defined in the claims or the use of such copolymers in PSAcompositions. The following discussion is intended to assist the readerin understanding related copolymer art.

According to Odian, Principles of Polymerization, 2nd Ed.,Wiley-Interscience, p. 18, (1981) polymers fall into three structuralgroups: linear, branched and crosslinked. Branched polymer molecules arethose in which there are side branches of linked monomer protruding fromvarious central branch points along the main polymer chain and that haveseveral idealized configurations. Branched polymers are known in atleast three configurations. They may be "comb-like" where each branch isof equal length, "dendritic" where branches occur on branches (seriesbranching), or "star-like" where all branches radiate from a singlepoint.

Branching often imparts various desirable properties, for example,branched polymers have been made that have improved melt flow andprocessability. Additionally, appropriate branching disrupts long linearpolymer backbones to thereby reduce crystallinity. In free radical andcationic polymerization processes, for example in the production ofpolyethylene, branching is largely uncontrolled and its extent isdependent on polymerization variables. In some cases branching can be ashigh as 15-30 branches per 500 monomer units. In contrast, anionicpolymerization processes yield very narrow molecular weightdistributions and a unique structure. Branched polymer structuresproduced by anionic polymerization are generally star shaped (arrayedabout a central point or nucleus) although the structure can be variedby coupling together individually prepared arms of different structure.

Such polymers are described by St. Clair in U.S. Pat. No. 4,391,949where "asymmetric" star block copolymers are prepared by mutuallylinking together individually prepared living polymers, which may berepresented by (AB)Li and (C)Li, with polyalkenylaromatic linkingreagents. The structural formula describing the resulting polymer isgiven as (A--B)_(x) --Y--(C)_(z), where x plus z is greater than six. Astatistical distribution of polymer products would be obtained from thisprocess, where the average structure is equal to the mole ratio of therespective charges. Further chain growth would only be possible throughthe linking nucleus Y.

Crossland, U.S. Pat. No. 4,010,226, has also recognized the problem ofpreparing block polymers with an asymmetric configuration and, to avoidthe statistical distribution of polymers obtained by St. Clair, firstcoupled a set of polymer arms with divinylbenzene, then continued thepolymerization, utilizing the anionic centers that remain on thedivinylbenzene residue, to produce a different set of arms bound to thesame nucleus. The number of new arms grown would thus equal the numberof arms coupled together, since linking with divinylbenzene (DVB) is anon-terminating process and each newly grown arm would have an anionicterminus. Fahrbach, U.S. Pat. No. 4,086,298, discloses star-blockcopolymers having a mixture of arms where some arms are formed by firstpolymerizing styrene with alkyllithium to form living polymer blocks,represented by (A)Li, and then adding a mixture of styrene and butadieneto form a graded copolymer represented by A-B→A' where the arrowrepresents a graded segment. Other arms are made up of only thebutadiene-styrene graded copolymer segment. These arms are then linkedtogether with a polyfunctional coupling agent, such as DVB, to givestar-branched polymers. U.S. Pat. Nos. 4,221,884, 4,248,980, 4,248,982,4,248,983, and 4,248,984, Bi and Milkovich, describe a similar series ofpolymers in which more complex polymer arm segments are linked togetherusing a polyalkenyl aromatic, such as divinylbenzene, to form anasymmetric star molecule.

Prudence (U.S. Pat. No. 3,949,020) prepares branched block polymers by amethod wherein divinylbenzene is added with the diolefin monomer to apolystyryllithium initiator. However, according to Bi and Fetters(Macromolecules 9, 732-742 [1976]), such a method leads to gelation whenthe divinylbenzene/initiator ratio is three or greater.

Martin, in U.S. Pat. Nos. 4,080,400, 4,143,089, 4,148,838, and4,273,896, describes a composition obtained from the linking together ofanionically active polymers (from, e.g., styrene) with silanes of theformula, X_(4-a-b) Si(R)_(b) (CH═CH₂)_(a), where X is a displaceablegroup, R is alkyl, a is 1 to 4 and b is 1 to 3. One of the statedobjects of these patents is to couple polymeric carbanions with silanesand then form new carbanions which can be used to initiate thepolymerization of cyclic silicones or "other unsaturated monomers". Nodisclosure is provided directed towards the step of using otherunsaturated monomers except for certain unspecified hydrocarbon/siloxaneblock polymers.

It has been established [Nametkin, Chemical Abstract Nos. 85:47314a(1976), 87:185046g (1977), and 89:110569n (1978)]that vinylsilanes ofthe type described by Martin will copolymerize in an anionic fashion,for example with butadiene; however, reactivity is very low, with up to300 hours required for good conversion. Furthermore, copolymers of vinylsilanes with dienes initiated by butyl lithium are unimodal but exhibitpeak broadening due to the occurrence of chain termination reactionscaused by spontaneous cleavage reactions producing lithium hydride(Nametkin, Chemical Abstract No. 93:168679x, 1980). Loss of LiH duringanionic homopolymerization of vinyltrimethylsilane has also beenobserved and has been used to explain the poor conversion and spread inmolecular weight distribution observed in these polymers [Nametkin,Dokl. Nauk SSSR, 215, 861 (1974)]. Chaumont [Eur. Poly. J. 15, 537(1979)]prepared vinylsilyl terminated polystyrenes via anionicpolymerization; however, it was necessary to cap the polymer anion withdiphenylethylene in order to reduce side reactions.

Chlorosilane-substituted styrenes are well-known compounds and have beenused, for example, to prepare polysiloxane macromolecular monomers[Kawakami, Polymer J., 14, 913 (1982)]. Chromatography gels have beendescribed based on poly-α-methylstyrene dianions andchlorodimethylsilylstyrene [Greber, Angew. Makromol. Chem. 1971, 16/17,325]. Compositions for the encapsulation of electrical equipment havebeen derived from organosilicon monomers having styrenyl groups (Lewis,U.S. Pat. No. 2,982,757). Hirao et al. (Macromolecules 1987, 20, 242)has studied the anionic homopolymerization of (4-alkoxysilyl) styrenesand reaction of the resultant homopolymer with polystyryllithium.

There has been no disclosure, however, of the use oforganometallic-substituted styrenes, e.g., chlorosilanesubstitutedstyrenes, in the preparation of condensed phase polymers or of PSAcompositions made therewith.

SUMMARY OF THE INVENTION

The present invention provides pressure-sensitive adhesive compositionscomprising as a rubbery base material elastomeric copolymers and blockcopolymers, e.g., based upon styrene/isoprene, having a novel condensedphase structure wherein polymer branches occur along the polymerbackbone, either at a predetermined location or at random locations. Thepolymers are made by a method which comprises the step of reacting,under polymerization conditions, hydrocarbyl lithium initiator, at leastone anionically polymerizable compound, and an organometallicsubstitutedstyrene condensing agent. The reactants may be added simultaneously toproduce a copolymer with polymer branch segments randomly located alongthe polymer backbone or sequentially to produce a copolymer withbranches located at the same predetermined location along the polymerbackbone. The resultant polymers may be further reacted with a linkingagent to form multi-arm copolymers. The copolymers and their method ofpreparation are respectively claimed in U.S application Ser. Nos.107,292, and 107,262, filed 10/9/87, now U.S. Pat. No. 4,857,618, nowU.S. Pat. No. 4,857,615.

The resultant elastomeric polymers are compatible with any of a widevariety of known tackifier resins and plasticizers to produce uniquepressure-sensitive adhesive (PSA) compositions having unexpectedly lowmelt viscosities and, thus, excellent melt processability. In addition,the PSAs of this invention show improved high temperature shear adhesionrelative to their linear counterparts, with the shear strength exhibitedby condensed phase diblock polymer PSAs being particularly surprising inview of the tensile properties of the base polymers.

Specifically, the method comprises the step of reacting, underpolymerization conditions, the following:

(a) hydrocarbyl lithium initiator;

(b) at least one anionically polymerizable compound; and

(c) a condensing agent having the general formula

    CH.sub.2 ═C(R')QY(R).sub.n (X).sub.m                   I

wherein

Y is tetravalent Si, Ge, Sn or Pb;

X is H, --OR", Cl, Br or F wherein R" is a monovalent lower alkyl grouphaving from 1 to 6 carbon atoms;

R is hydrogen, a monovalent lower alkyl group having from 1 to 6 carbonatoms, or phenyl;

Q is phenylene;

R' is hydrogen, a monovalent lower alkyl group having from 1 to 6 carbonatoms, or phenyl;

m is an integer of 1, 2, or 3; and

n is an integer equal to 3-m, in a mole ratio of (a) to (c) of about (1+m):1 to form a condensed phase copolymer.

The elastomeric polymers are anionic copolymers comprising at least oneanionically polymerizable monomer and a condensing agent (I) monomerwherein the mole percentage of condensing agent (I) in each copolymersegment containing the condensing agent (I) is in the range of about0.01% to about 5%.

The polymers are generally copolymers of the condensing agent (I) withconjugated diene monomer, or are block copolymers of conjugated dieneand vinyl aromatic monomers (wherein at least one block is a copolymerof condensing agent monomer and either diene or vinyl aromatic monomer).The monovinyl aromatic monomer yields a hard polymer segment having ahigh T_(g), i.e., above 25° C. The conjugated diene monomer yields asoft (generally elastomeric) polymer segment having a low T_(g), i.e.,not greater than about 0° C.

The polymers of the PSA compositions of the invention are preferablyelastomeric anionic polymers comprised of conjugated diene monomer,typically containing 4 to 12 carbon atoms, monoalkenyl or monovinylaromatic monomer and the condensing reagent (I) wherein the mole percentof condensing reagent in a polymer segment containing such reagent isabout 0.01 to about 5.0, preferably about 0.02 to about 2.0. Typically,the copolymer contains on a weight basis from about 50% to about 90%conjugated diene and about 50% to about 10% monoalkenyl or vinylaromatic monomer.

In one embodiment, branch points are introduced at predetermined loci inthe polymer chain by addition of condensing agent in a sequentialfashion, i.e., after formation of a living polymer segment viaconventional anionic polymerization techniques. Thus, copolymer isprepared by first forming a living linear polymer segment, then reactingthe living polymer segment with the condensing reagent to form acondensed living copolymer and next polymerizing therewith additionalpolymerizable compound to form a condensed phase block copolymer. Such ablock copolymer may be represented by the following general formula:

    (A).sub.z Z.sub.q --B                                      II

where:

A is a nonelastomeric polymer segment based on a monovinyl aromaticcompound such as styrene, alpha-methylstyrene, para-methylstyrene, andt-butyl styrene;

B is an elastomeric polymer segment based on a conjugated dienecompound, such as butadiene,isoprene, and piperylene;

Z is the residue of a condensing reagent having the general formula

    CH.sub.2 ═C(R')QY(R).sub.n (X).sub.m                   I

where X, R, Y, Q, R', m and n have been defined above;

q is an integer from 1 to about 10;

x is an integer from 2 to about 10; and

wherein the mole percentage of Z in the segment (A)_(x) Z_(q) is in therange of about 0.1% to about 5%.

The method comprises the further step of contacting the resultingcondensed phase block copolymer of Formula II with a multifunctionallinking agent such as a polyalkenyl aromatic linking agent underreactive conditions thereby forming a multi-arm condensed phase blockcopolymer. Such a block copolymer may be represented by the followinggeneral formula:

    [(A).sub.x Z.sub.q--B].sub.y L.sub.z                       III

where:

A, Z, B, x, and q have been defined above;

L is the residue of a multifunctional linking agent;

z is an integer from zero to about 10;

y is an integer from 1 to about 50 and, when y is 1, z is zero;

wherein the mole percentage of Z in the segment (A)_(x) Z_(q) is in therange of about 0.1% to about 5%.

The method also comprises first forming a living linear polymer segment,adding a second polymerizable compound to form a living linear blockcopolymer segment, then reacting the living linear block copolymersegment with the condensing reagent to form a condensed living blockcopolymer, and next polymerizing therewith additional polymerizablecompound to form a condensed phase block copolymer represented by thefollowing general formula:

    (A--B).sub.x Z.sub.q --B                                   IV

where:

A, B, Z, x and q are defined above and wherein the mole percentage of Zin the segment (A--B)_(x) Z_(q) is in the range of from about 0.01% toabout 1%.

The method comprises the further step of contacting resulting blockcopolymer IV with a multifunctional linking agent under reactiveconditions thereby forming a multi-arm condensed phase block copolymerrepresented by the general formula shown below:

    [(A--B).sub.x Z.sub.q --B].sub.y L.sub.z                   V

wherein:

A, B, Z, L, x, q, y and z are defined above and wherein the molepercentage of Z in the segment (A--B)_(x) Z_(q) is in the range of about0.01% to about 1%.

Other condensed phase block copolymers besides II and IV are alsocontemplated and may be linked to form multi-arm condensed phase blockcopolymers other than III and V. Such block copolymers, including II,III, IV, and V, may be represented by the general formula:

    [(W).sub.x Z.sub.q --W'].sub.y L.sub.z                     VI

wherein:

W is selected from the group consisting of A, B, BA, and AB, W' isselected from the group consisting of B, BA and AB, and A, B, Z, L, x,q, y and z are defined above, and wherein the mole percentage of Z inthe segment (W)_(x) Z_(q) is in the range of from about 0.01% to about5%.

In a second embodiment, randomly placed branch centers are generated onthe polymer chain by polymerization of a mixture of condensing agent andanionically polymerizable monomer or monomers. The method involvessimultaneously reacting a hydrocarbyl lithium initiator, polymerizablecompound, and condensing reagent to form a living condensed phasecopolymer having a randomly-branched structure which may be representedby the following general formula:

    B/Z                                                        VII

wherein B and Z are defined above, and wherein the mole percentage of Zin the copolymer is from about 0.01% to about 1%.

Copolymer VII may be further reacted with a multifunctional linkingagent, thereby forming a multi-arm condensed phase copolymer. Such acopolymer may be represented by the general formula:

    (B/Z).sub.y L.sub.z                                        VIII

wherein B, Z, L, y and z are defined above, and wherein the molepercentage of Z in the unlinked copolymer is from about 0.01% to about1%.

Monovinyl aromatic monomer may be polymerized with condensing reagent toform a randomly-branched living copolymer which may be further treatedby adding a different polymerizable compound such as butadiene,isoprene, or piperylene, after completion of the simultaneous reactionand permitting the different polymerizable compound to copolymerize withthe living copolymer to form a condensed phase block copolymer. Theresultant copolymer may be further reacted with a multi-functionallinking agent thereby forming a multi-arm condensed phase blockcopolymer. Such block copolymer may be represented by the generalformula:

    [(A/Z)--B].sub.y L.sub.z                                   IX

wherein A, B, Z, L, y and z are defined above, and wherein the molepercentage of Z in the segment A/Z is in the range of from about 0.1% toabout 5%.

In addition, a randomly-branched living copolymer derived from monovinylaromatic monomer may be further treated by adding a mixture of adifferent polymerizable compound and additional condensing reagent,after completion of the simultaneous reaction, and permitting themixture to copolymerize with the living copolymer to form a blockcopolymer having "condensed" structure randomly placed in both blocks.This block copolymer may be further reacted with a multifunctionallinking agent under reactive conditions thereby forming a multi-armcondensed phase block copolymer. Such a block copolymer may berepresented by the general formula:

    [(A/Z)--(B/Z)].sub.y L.sub.z                               X

wherein A, B, Z, L, y and z are defined above, and wherein the molepercentage of Z in the segment A/Z is in the range of from about 0.1% toabout 5% and in the segment B/Z is from about 0.01% to about 1%.

Alternatively, a different condensed phase block copolymer may beprepared by first forming a living linear polymer segment, adding amixture of a second polymerizable compound and the condensing reagent,and then permitting the mixture to copolymerize with the living linearpolymer segment produced by polymerization of the first polymerizablecompound. The resulting block copolymer may be further modified bycontacting it with a multifunctional linking agent under reactiveconditions thereby forming a multi-arm condensed phase block copolymer.Such a block copolymer may be represented by the general formula:

    [A--(B/Z)].sub.y L.sub.z                                   XI

wherein A, B, Z, L, y and z are defined above, and wherein the molepercentage of Z in the segment B/Z is in the range of from about 0.01%to about 1%. The unlinked block copolymer may be alternatively modifiedto include an additional linear polymer segment to provide a blockcopolymer which may be represented by the general formula

    A--(B/Z)--A                                                XII

wherein A, B and Z are defined above.

The invention provides pressure-sensitive adhesive compositionscomprising at least one of copolymers II-XI and sufficient compatibletackifier resin to endow the composition with adhesive tack, as well assheet materials comprising a backing having at least one major surfacethereof at least partially coated with such pressure-sensitive adhesivecomposition.

BRIEF DESCRIPTION OF DRAWINGS

Understanding of the invention will be facilitated by reference to thedrawings, wherein:

FIGS. 1 and 2 are graphs depicting the melt viscosity of untackified andtackified polymers according to the invention and a styrene isoprenelinear triblock copolymer (Shell's Kraton® 1107) according to the priorart as a function of shear rate; and

FIG. 3 is a graph depicting the steady shear viscosity of polymeraccording to the invention and a styrene isoprene linear triblockcopolymer (Shell's Kraton® 1107) according to the prior art as afunctionof shear rate.

DETAILED DESCRIPTION

The initiators useful in the preparation of the copolymers used in thePSA compositions of this invention are known alkyllithium compounds suchas methyllithium, n-butyllithium and sec-butyllithium, cycloalkyllithiumcompounds such as cyclohexyllithium, and aryllithium compounds such asphenyllithium, naphthyllithium and the like.

Useful monoalkenyl aromatic monomers include styrene, ring-substitutedstyrenes, and alpha-substituted styrenes. These can be used individuallyor as mixtures. Preferred are styrene, alpha-methylstyrene,paramethylstyrene, and t-butylstyrene. Useful conjugated diene monomershave 4 to 12 carbon atoms, e.g., 1,3-butadiene, isoprene, piperylene,myrcene, 2,3-dimethylbutadiene, and the like. These also may be usedindividually or as mixtures. Preferred conjugated diene monomers are1,3-butadiene, isoprene, and piperylene.

The "condensed phase" or branch structure of the copolymers of thisinvention is formed by addition of a multifunctional "condensing"reagent to create points at which two or more polymer segments areconnected together by the reagent. The terminology "condensed" isderived from the term "polycondensation" which, according to ChemicalKinetics edited by C.H. Bamford (Elsevier, 1976), is used to denotethose polymerization reactions which proceed by a propagation mechanismin which an active polymerization site disappears every time one monomerequivalent reacts. Also, Webster's 7th Collegiate Dictionary definescondensation as a chemical reaction involving union between atoms in thesame or different molecules often with elimination of a simple moleculeto form a more complex compound of often greater molecular weight. Itshould be pointed out that the linking processes that occur with"condensing" reagents and linking agents such as divinylbenzene are verydifferent. "Condensing" reagents yield a polymeric species with a singleanionic charge, whereas divinylbenzene joins polymer segments togetherto give a nucleus containing a number of anions equal to the number ofchains linked together. Thus, the potential for network formation andgelation associated with the method of Prudence is avoided by use of"condensing", rather than linking, agents.

Suitable condensing agents are compounds having dual functionality, thefirst derived from at least one anionically polymerizable group and thesecond from at least one other group capable of undergoing one or morenucleophilic displacement reactions. One active chain is terminated byeach nucleophilic displacement reaction. The relative reactivity of thetwo groups is unspecified, such that anion addition may be faster orslower than termination, and the preference of relative reactivity forthe two groups will depend on the final polymer structure desired. Thecondensing agent must be compatible with anionic polymerizationprocesses; i.e., its anionically polymerizable group(s) should becapable of reinitiating polymerization of itself or other anionicallypolymerizable monomers. Useful condensing agents are molecules of thefollowing structure: ##STR1## wherein

Y is tetravalent Si, Ge, Sn, or Pb;

X is H, --OR", Cl, Br, or F, wherein R" is a monovalent lower alkylgroup having from 1 to 6 carbon atoms;

R is hydrogen, a monovalent lower alkyl group having from 1 to 6 carbonatoms, or phenyl;

R' is hydrogen, a monovalent lower alkyl group having from 1 to 6 carbonatoms, or phenyl;

m is an integer of 1, 2, or 3; and

n is an integer equal to 3-m.

The displaced group, X, does not subsequently react in a side reactionwith polymer anions. The alkenylaromatic group may be substituted in thealpha position with alkyl or aromatic moieties, R', to modify condenserreactivity. The alkenylaromatic group may also be further substituted onthe aromatic ring with groups such as alkyl, phenyl, alkoxy,dialkylamino, and the like, which are not reactive toward polymeranions. Preferred condensing agents are the silylstyrenes for which R ismethyl, R, is hydrogen, Y is silicon, and X is F, Cl, Br, or methoxy,or, most preferably, X is F or Cl.

The above-described condensing agents are readily prepared via an insitu Grignard reaction involving, e.g., para-chlorostyrene andchloroalkylsilane. Other routes for the preparation of these compoundshave been described by Chernyshev (Chemical Abstracts 62:6502c). Thecondensing agents are utilized to achieve a branched or condensed phasepolymer structure by addition of 1/n mole of multifunctional condenserper mole of active polymer anions, where n is the total number ofanionically reactive sites on the condenser molecule. The molepercentage of condensing agent monomer in any particular polymer segmentis generally within the range of from about 0.01% to about 5%,preferably, within about 0.02% to about 2%. (For monovinyl aromatics,the range is about 0.1-5%, with about 0.2-2% preferred; for conjugateddienes, the range is about 0.01-1%, with about 0.02-0.2% preferred.)

Conventional anionic polymerization techniques are utilized in preparingthe condensed phase polymers for use in the PSA compositions of thisinvention. Thus, the polymerization is carried out in an inertatmosphere in the absence of moisture, air, or other impurities whichare known to react with polymer anions. A temperature between 0° C. and100° C., more preferably between 30° C. and 80° C., is maintained.Suitable solvents are hydrocarbon solvents which may be aliphatic,cycloaliphatic, or aromatic. Optionally, ethers such as tetrahydrofuran,diethylether, or other similar solvents, may be used either alone or asmixtures with the hydrocarbon solvent.

If so desired, linking agents may be used to increase the degree ofbranching of the condensed phase copolymers or block copolymers beyondthat achieved via the condensing agent. In this way, symmetrical polymerarchitectures such as radial or star structures, etc., can be created,the final structure being a function of the linking molecule. Suchmultifunctional linking agents are well-known in the art and aredetailed, e.g., in U.S. Pat. No. 3,985,830. Preferred examples of suchcompounds are 1,2-dibromoethane, silicon tetrachloride, dichlorodimethylsilane, phenyl benzoate, and divinylbenzene. The quantity of linkingagent used to further combine the anionically-terminated species of thisinvention is derived from the actual content of active polymer chainends in the polymerization mixture. Generally, a mole equivalent oflinking agent to chain ends is required when the agent links polymerchain ends by termination reactions, as is the case for, e.g.,dibromoethane and silicon tetrachloride. When non-terminating agentssuch as divinylbenzene are utilized to form star polymers, higher moleratios are used, generally within the range of from about 3:1 to about20:1 or higher. The preferred range is from about 3:1 to about 8:1.

The molecular weights of the condensed phase polymers may be varied tosuit an individual application. When conjugated diene monomers areutilized, preferred molecular weights are generally in the range of fromabout 50,000 to about 200,000. In the case of additional linking ofthese copolymers via, e.g., divinylbenzene to form star polymers,molecular weights may exceed 1,000,000. Condensed phase block copolymerscan have individual segment molecular weights that are typicallypreferred in the art, i.e., from about 5,000 to about 50,000 for theglassy or hard monoalkenyl aromatic phase and from about 50,000 to about250,000 for the elastomeric or rubbery conjugated diene phase.

Both the conjugated diene-based condensed phase copolymers and thecondensed phase block copolymers (and linked structures derived fromeach) are useful in preparing PSA compositions. The block copolymersutilized for this purpose typically have a hard phase content of fromabout 10% to about 30% by weight (the remainder constituting the rubberyphase). The PSA compositions of this invention may be formed by mixingcondensed phase copolymer or block copolymer and tackifying resin,either in solution, as dry granules, or by melt blending. Any of theresinous (or synthetic) materials commonly used in the art to impart orenhance the tack of PSA compositions may be used as a tackifier.Examples include rosin, rosin esters of glycerol or pentaerythritol,hydrogenated rosins, polyterpene resins such as polymerized β-pinene,coumaroneindene resins, "C5" and "C9" polymerized petroleum fractions,and the like. The use of such tack-modifiers is common in the art, as isdescribed in the Handbook of Pressure-Sensitive Adhesive Technologyedited by Donatas Satas (1982). Tackifying resin is added in an amountsufficient to provide a tacky composition. This is typically achieved byadding from about 50 parts to about 300 parts by weight of tackifyingresin per 100 parts by weight of condensed phase copolymer.

The tackifier resin is selected to provide the copolymers with anadequate degree of tack to maintain in the resultant compositionbalanced PSA properties including high shear and peel. As is known inthe art, not all tackifier resins interact with the same base elastomerin the same manner; therefore some minor amount of experimentation maybe required to select the appropriate tackifier resin and to achieveoptimum adhesive performance. Such minor experimentation is well withinthe capability of one skilled in the adhesive art. Along these lines,selection of the resin should take into account whether the resinassociates with the thermoplastic styrene segment or the rubberysegments.

It is also within the scope of this invention to include various othercomponents in the adhesive formulation. For example, it may be desirableto include such materials as plasticizers, pigments, fillers,stabilizers, and/or various polymeric additives.

The PSA compositions of this invention can be applied as solutions,dispersions, or as hot melt coatings to suitable flexible or inflexiblebacking materials to produce PSA-coated sheet materials. Flexiblebackings may be of any material which is conventionally utilized as atape backing or may be of any other flexible material. Representativeexamples of flexible tape backing materials include paper, plastic filmssuch as poly(propylene), poly(ethylene), poly(vinyl chloride), polyester[e.g., poly(ethylene terephthalate)], cellulose acetate, and ethylcellulose. Backings may also be of woven fabric formed of threads ofsynthetic or natural materials such as cotton, nylon, rayon, glass, orceramic material, or they may be of a nonwoven fabric such as air-laidwebs of natural or synthetic fibers or blends of these. In addition, thebacking may be formed of metal, metallized polymeric film, or ceramicsheet material. The PSA-coated sheet materials may take the form of anyarticle conventionally known to be utilized with PSA compositions suchas labels, tapes, signs, covers, marking indices, and the like.

The PSA compositions of this invention may be coated by any of a varietyof conventional coating techniques such as roll coating, knife coating,or curtain coating. The PSA compositions may also be coated withoutmodification by extrusion, coextrusion, or hot melt techniques byemploying suitable conventional coating devices for this purpose.Because of the unique rheological characteristics of the condensed phasepolymers and their blends with tackifiers, hot melt coating isparticularly preferred. Primers may be utilized, but they are not alwaysnecessary.

EXAMPLES

The invention is illustrated by the following examples, wherein allparts are by weight unless otherwise indicated.

Nomenclature and Symbols

"S_(10M) is a short-hand designation for a polymer segment consisting ofpolystyrene(S) having a molecular weight of 10,000 (10M). Other polymersegments are identified in a similar manner with the first letterrepresenting the first letter of the monomer of the polymer segment andthe subscript indicating the molecular weight in thousands, e.g., 10Mwould mean a 10,000 molecular weight. As a further example, I_(120M)represents a polymer segment based upon isoprene which has a molecularweight of 120,000.

"br/n" refers to the fact that the polymer is randomly branched,indicated by "br", and "n" is an integer expressing the functionality ofthe condensing agent monomer. The term "br/n" is used as a prefix forthe polymer segment modified. For example, S_(10M) -br/2-I_(120M)represents a block copolymer having a linear 10,000 molecular weightpolystyrene segment (S_(10M)) and a randomly branched 120,000 molecularweight polyisoprene segment (br/2-I_(120M)).

Gel Permeation Chromatography

A Hewlett-Packard Model 1084B high performance liquid chromatographequipped with two bimodal Zorbax PSM Kits (two columns at 60-S Å and twocolumns at 1000-S Å) was used for all determinations. Samples weredissolved in THF (AR grade) and filtered through a 0.5 micrometerpolytetrafluoroethylene filter. Samples were injected at volumes of 10microliters and eluted at a rate of 0.5 ml per minute through thecolumns maintained at 40° C. THF (AR grade) was used as the solvent. Thedifferential refractometer detector was a Hewlett-Packard Model 1037A.The system was calibrated using polystyrene standards and employing alinear least squares fit. All GPC calculations were performed on an IBM9000 integrator and all molecular weight averages are polystyreneequivalent molecular weights. The molecular weight averages werecalculated according to accepted practices. GPC test methods are furtherexplained in Modern Size Exclusion Liquid Chromatography by W. W. Yau,J. J. Kirkland, and D. D. Bly, John Wiley and Sons, 1979.

PSA Test Methods

The test methods which were used to evaluate PSA-coated flexible sheetmaterials are industry standard tests. The standard tests are describedin various publications of the American Society for Testing andMaterials (ASTM), Philadelphia, Pa., and the Pressure Sensitive TapeCouncil (PSTC), Glenview, Ill., and are detailed below. The referencesource of each of the standard test methods is also given.

Shear Adhesion

Reference: ASTM: D3654-78; PSTC-7

The shear adhesion strength is a measure of the cohesiveness or internalstrength of an adhesive. It is based upon the amount of force requiredto pull an adhesive strip from a standard flat surface in a directionparallel to the surface to which it has been affixed with a definitepressure. It is measured in terms of time (in minutes) required to pulla standard area of adhesive coated sheet material from a stainless steeltest panel under stress of a constant, standard load.

The tests were conducted on adhesive-coated strips applied to astainless steel panel such that a 12.7 mm by 12.7 mm portion of eachstrip was in firm contact with the panel with one end portion of thetape being free. The panel with coated strip attached was held in a racksuch that the panel forms an angle of 178° with the extended tape freeend which is then tensioned by application of a force of one kilogramapplied as a hanging weight from the free end of the coated strip. The2° less than 180° is used to negate any peel forces, thus insuring thatonly the shear forces are measured, in an attempt to more accuratelydetermine the holding power of the tape being tested. The time elapsedfor each tape example to separate from the test panel is recorded as theshear adhesion strength.

Peel Adhesion

Reference: ASTM D3330-78 PSTC-1 (11/75)

Peel adhesion is the force required to remove a coated flexible sheetmaterial from a test panel measured at a specific angle and rate ofremoval. In the examples, this force is expressed in Newtons per 100 mm(N/100 mm) width of coated sheet. The procedure followed is:

1. A 12.7 mm width of the coated sheet is applied to the horizontalsurface of a clean glass test plate with at least 12.7 lineal cm in firmcontact. A 2 kg hard rubber roller is used to apply the strip.

2. The free end of the coated strip is doubled back nearly touchingitself so the angle of removal will be 180° . The free end is attachedto the adhesion tester scale.

3. The glass test plate is clamped in the jaws of a tensile testingmachine which is capable of moving the plate away from the scale at aconstant rate of 2.3 meters per minute.

4. The scale reading in Newtons is recorded as the tape is peeled fromthe glass surface. The data is reported as the average of the range ofnumbers observed during the test.

EXAMPLES 1-23

The type and amount of each material used in each reaction, as well asthe resultant polymer composition, are shown in Tables I-III forExamples 1-23.

A 5-liter, 5-necked reaction flask equipped with stirrer, condenser(under a small positive argon pressure from a gas bubbler), thermometer,and 3-septum inlet was used in the procedures which follow. Allglassware and fittings were baked at 120+° C. for a minimum of 24 hours,were assembled under argon while hot, and then the entire apparatus wasflamed under argon purge. Transfers of solvent and isoprene were madethrough stainless steel needles (through rubber septa) connected withpolytetrafluoroethylene (Teflon®) tubing from a tared vessel orcontainer using argon pressure. Styrene monomer was transferred througha rubber septum via syringe. Cyclohexane (AR grade) was dried by storagefor 96+ hours over indicating 4-6 mesh silica gel, and styrene monomerwas dried by chromatography on a 1 cm×15 cm two-layered alumina (150mesh)/silica gel (28-200 mesh) column. Purification of isoprene wasinitiated by stirring with KOH pellets for a minimum of two hours,followed by removal of the KOH by filtration. The isoprene was thenrefluxed over CaH₂ granules and, finally, was distilled and collectedunder argon in 500 g portions which were stored at 0-5° C.Divinylbenzene (Matheson, Coleman, and Bell (MCB), 56% commercial grade)was purified by chromatography on a chilled, two-layered alumina (150mesh)/silica gel (28-200 mesh) column (approximately 1 cm×15 cm)immediately before use. sec-Butyl lithium (Lithium Corporation ofAmerica, 12% in cyclohexane) was used as received from freshly openedbottles and was transferred via syringe through a rubber septum. Alkoxy-or haloalkylsilylstyrene condensing agents were prepared under nitrogenby the method descibed in the Detailed Description above, were distilledand sealed (in glass ampoules) under vacuum, and were then refrigeratedat 0°-5° C.

In each example described below, the following preliminary glassware"sweetening" process was carried out prior to polymerization: 0.3 mlstyrene was added to cyclohexane (an amount equal to the tabulatedamount of cyclohexane minus the amount required to additionally preparea 50% solution of the tabulated amount of isoprene), the mixture wasthen heated to 55°-60° C., and 3.0 ml of 1.3M sec-butyl lithium wereadded to obtain a bright orange color. The solution was then kept underreflux for about 45 minutes, cooled to 60° C., and back-titrated withcyclohexane saturated with methanol until the color just disappeared.

EXAMPLES 1 AND 2

These examples demonstrate the preparation of polymers having randombranching in the vinyl aromatic phase. Table I details reactant amountsand product compositions for polymers made via the following generalprocedure.

After the glassware "sweetening" process (while still at 60° C.), thefull charge of styrene (as indicated in Table I) was added and titratedwith 1.3M sec-butyl lithium to a pale yellow color. Then the fullsec-butyl lithium initiator charge (as indicated in Table I) was added.Exactly one minute after the sec-butyl lithium addition, neatchloroalkylsilylstyrene condensing agent was added by injection througha rubber septum, and the reaction mixture was then stirred and kept at60° C. for one hour. The reaction was continued by adding a 50% solutionof isoprene (quantity shown in Table I) in cyclohexane which had beenpassed through a 4 cm×20 cm column of 28-200 mesh silica gel (minimumresidence time of 30 minutes). The reaction mixture was then allowed topolymerize for three hours at 60°-65° C. During the initial exotherm, acold water bath was necessary to prevent excessive reflux and loss ofisoprene. Finally, star block copolymer was formed by addingdivinylbenzene linking agent in one portion via syringe (through arubber septum) and allowing polymerization over several hours at 60°-65°C. before termination with 1 ml of degassed methanol. The reaction flaskwas then allowed to cool to room temperature, was opened, and 3.5% byweight of solids of octadecyl-3,5-di-tert-butyl-4-hydroxyhydrocinnamateantioxidant and thermal stabilizer (Ciba Geigy Irganox® 1076) wasimmediately added as a polymer stabilizer. Next, precipitation of thepolymer was achieved by slow addition of the polymer syrup to agitatedisopropanol, followed by air drying or drying in a vacuum oven at 40° C.The yield was essentially quantitative, and weight average molecularweights were determined (by size exclusion gel permeation chromatographyas described above) to be as shown in Table I.

Tables I-III display quantities of styrene and isoprene in grams, withamounts of initiator and condensing agent in millimoles. Although thisappears to be inconsistent, it is done to show the relationship amongreactant amounts, amount of initiator or condensing agent, and molecularweight.

                                      TABLE I                                     __________________________________________________________________________    RANDOMLY-BRANCHED STYRENE                                                                                                           MW                                                                                 No. of.1                            kg      g  g   Condensing       MW of.sup.1                                                                        Prod-                                                                              Arms.sup.2         Ex.              cyclo-                                                                            mmol                                                                              sty-                                                                             iso-                                                                              agent*   Linking agent**                                                                       AB ×                                                                         uct                                                                                permes.            No.                                                                              Polymer       hexane                                                                            BuLi                                                                              rene                                                                             prene                                                                             Type mmol                                                                              Type                                                                              mmol                                                                              10.sup.-3                                                                          10.sup.-3                                                                          Star               __________________________________________________________________________    1  (br/2-S.sub.10M --1.4-I.sub.60M).sub.n DVB                                                  1.4 4.29                                                                              21.4                                                                             128.6                                                                             SSCL 2.14                                                                              DVB 12.8                                                                              101  853  8                  2  (br/2-S.sub.10M --1.4-I.sub.60M).sub.n DVB                                                  1.9 5.80                                                                              28.5                                                                             171.5                                                                             m-SSCL                                                                             2.90                                                                              DVB 17.4                                                                              126  918  7                  __________________________________________________________________________     *SSCL = 4(chlorodimethylsilyl)styrene                                         mSSCL = 3(chlorodimethylsilyl)styrene                                         **DVB = divinylbenzene                                                        .sup.1 Weight average molecular weight: polystyrene equivalent as             determined by size exclusion gel permeation chromatography.                   .sup.2 Ratio of MW (product) to MW (AB)                                  

EXAMPLES 3-14

These examples demonstrate the preparation of polymers having randombranching in the rubbery diene phase. Table II details reactant amountsand product compositions for polymers made via the following generalprocedure.

After the glassware "sweetening" process, the full charge of styrene (asindicated in Table II) was added, followed by the initiating dose ofsec-butyl lithium. The temperature was maintained at 60° C. for onehour. The alkoxy- or haloalkylsilylstyrene condensing agent was thenadded to a 50% solution of isoprene (or, for example 12, butadiene) incyclohexane which had previously been passed through a column of silicagel as described above. This solution was added to the reaction flask(by argon pressure) through two stainless steel needles (through rubbersepta) connected with polytetrafluoroethylene (Teflon®) tubing. Thereaction temperature was maintained at 55°-60° C. at first by coolingand later by heating for three hours.

At this point, the reaction was terminated for examples 3, 4 and 10-14.Example 5 required the sequential addition of another charge of styrene(13 g) and maintaining the temperature at 55°-60° C. for another hourbefore termination. Star block copolymer was formed in Examples 6-9 byaddition of divinylbenzene that had been purified as describedpreviously. The temperature was then kept at 60° C. for several hoursbefore termination. In all cases, the polymerization was terminated bythe addition of 1 ml of degassed methanol followed by cooling,stabilization (by addition of 3.5% by weight of solids of Irganox®1076), precipitation in isopropanol, and drying, as described above.Molecular weights were determined to be as shown in Table II.

                                      TABLE II                                    __________________________________________________________________________    RANDOMLY-BRANCHED ISOPRENE                                                                                                          MW                                                                                 No. of.1                            kg      g  g   Condensing       MW of.sup.1                                                                        Prod-                                                                              Arms.sup.2         Ex.              cyclo-                                                                            mmol                                                                              sty-                                                                             iso-                                                                              agent*   Linking agent**                                                                       AB ×                                                                         uct  per                No.                                                                              Polymer       hexane                                                                            BuLi                                                                              rene                                                                             prene                                                                             Type mmol                                                                              Type                                                                              mmol                                                                              10.sup.-3                                                                          10.sup.-3                                                                          Star               __________________________________________________________________________    3  (S.sub.10M --br/2-1,4-I.sub.120M)                                                           1.7 4.29                                                                              42.9                                                                             257 SSCL 2.14                                                                              .   .        137  .                  4  (S.sub.10M --br/3-1,4-I.sub.184M)                                                           2.3 4.20                                                                              42 258 SSDCL                                                                              1.40                                                                              .   .        480  .                  5  (S.sub.10M --br/3-1,4-I.sub.278M --S.sub.10M)                                               2.29                                                                              2.60                                                                              26 241 SSDCL                                                                              0.87                                                                              .   .        589  .                  6  (S.sub.10M --br/2-1,4-I.sub.120M).sub.n DVB                                                 1.5 3.91                                                                              39 234 SSCL 1.96                                                                              DVB 11.8                                                                              176  915  5                  7  (S.sub.10M --br/3-1,4-I.sub.184M).sub.n DVB                                                 2.0 4.20                                                                              42 258 SSDCL                                                                              1.40                                                                              DVB 8.4 176  1.114                                                                              6                  8  (S.sub.5M --br/3-1,4-I.sub.184M).sub.n DVB                                                  2.6 4.20                                                                              21 258 SSDCL                                                                              1.40                                                                              DVB 8.4 155  1.063                                                                              7                  9  (S.sub.624 --br/3-1,4-I.sub.150M).sub.n DVB                                                 2.3 5.40                                                                              3.37                                                                             280 SSDCL                                                                              1.80                                                                              DVB 18  132  1.142                                                                              9                  10 S.sub.10M --br/2-1,4-I.sub.120M                                                             2.0 3.33                                                                              33.3                                                                             200 SSMO 1.67                                                                              .   .   .    Trimodal                                                                           .                  11 S.sub.10M --br/2-1.4-I.sub.120M                                                             2.0 3.33                                                                              33.3                                                                             200 SSF  1.67                                                                              .   .   .    212  .                  12 S.sub.10M --br/2-1.4-Bd.sub.120M                                                            2.9 3.57                                                                              35.7                                                                             214.3.sup.3                                                                       SSCL 1.79                                                                              .   .   .    260  .                  13 S.sub.10M --br/4-1.4-I.sub.240M                                                             2.1 3.33                                                                              33.3                                                                             200 SSTCL                                                                              0.833                                                                             .   .   .    570  .                  14 (S.sub.10M --br/2-1.4-I.sub.120M)                                                           2.2 4.15                                                                              41.5                                                                             249 SSBr 2.07                                                                              .   .   .    149  .                  __________________________________________________________________________     *SSCL = 4(chlorodimethylsilyl)styrene                                         SSDCL = 4(dichloromethylsilyl)styrene                                         SSBr = 4(bromodimethylsilyl)styrene                                           SSF = 4(fluorodimethylsilyl)styrene                                           SSTCL = 4(trichlorosilyl)styrene                                              SSMO = 4(methoxydimethylsilyl)styrene                                         **DVB = divinylbenzene                                                        .sup.1 Weight average molecular weight: polystyrene equivalent as             determined by size exclusion gel permeation chromatography                    .sup.2 Ratio of MW (product) to MW (AB)                                       .sup.3 Butadiene was employed in place of isoprene                       

EXAMPLES 15-23

These examples demonstrate the preparation of polymers havingpoint-branched structures. Table III details reactant amounts andproduct compositions for polymers made via the following generalprocedure.

After the glassware "sweetening" process, the full styrene charge (seeTable III) was added, followed by the sec-butyl lithium initiatingcharge. A temperature of 55°-60° C. was held for one hour.*

*For Examples 16-23, the chloroalkylsilylstyrene condensing agent wasinjected at this point (in one portion by syringe), and the temperaturewas maintained at 55°-60° C. for another 45 minutes. Then a purified 50%solution of isoprene in cyclohexane was added as described above, andthe reaction temperature was kept at 55°-60° C. for three hours, atfirst by cooling and later by heating. Finally, the divinylbenzene (orother) linking agent (as shown in Table III) was added and a temperatureof 60° C. maintained for several hours.

*For Example 15, 3/4 of a purified 50% solution of isoprene incycloexane was added at this point, and the temperature was held at55°-60° C. for 2 hours and 45 minutes. Then, the haloalkylsilylstyrenecondensing agent was added and the same temperature range maintained foranother 45 minutes, at which time the remaining 1/4 of the isoprenesolution was added and the temperature again held at 55°-60° C. for 2hours and 45 minutes. Lastly, the divinylbenzene linking agent was addedand a temperature of 60° C. maintained for several hours.

For all of these examples (15-23), termination was achieved via additionof 1 ml of degassed methanol, and, after cooling to room temperature,the polymer was stabilized, precipitated, and dried as described for theprevious examples. Molecular weights were as shown in Table III.

                                      TABLE III                                   __________________________________________________________________________    POINT BRANCHING                                                                                     kg cyclo-                                                                          mmol                                                                              g   g                                          Ex. No.                                                                            Polymer          hexane                                                                             BuLi                                                                              styrene                                                                           isoprene                                   __________________________________________________________________________    15   [(S.sub.10M --1,4-I.sub.38M).sub.3 --1,4-I.sub.38M ].sub.n DVB                                 2.3  6.00                                                                              60  300                                        16   [(S.sub.5M).sub.2 --1,4-I.sub.60M ].sub.n DVB                                                  1.9  8.00                                                                              40  240                                        17   [(S.sub.5M).sub.3 --1,4-I.sub.107M ].sub.n DVB                                                 2.3  8.61                                                                              43  307                                        18   [(S.sub.10M).sub.2 --1,4-I.sub.120M ].sub.n DVB                                                2.3  4.00                                                                              40  240                                        19   [(S.sub.10M).sub.2 --1,4-I.sub.120M ].sub.n DVB                                                2.3  6.20                                                                              53  372                                        20   [(S.sub.10M).sub.2 --1,4-I.sub.60M ].sub.2 DEPO                                                2.0  6.20                                                                              62  186                                        21   [(S.sub.10M).sub.2 --1,4-I.sub.60M ].sub.2 PB                                                  2.0  5.20                                                                              52  156                                        22   [(S.sub.10M).sub.2 --1,4-I.sub.60M ].sub.2 DBE                                                 1.4  3.75                                                                              37.5                                                                                112.5                                    23   [(S.sub.10M).sub.2 --1,4-I.sub.240m ]                                                          2.2  3.33                                                                              33.3                                                                              200                                        __________________________________________________________________________                           MW of.sup.1                                                                        MW of.sup.1                                                                         No. of                                      Condensing agent*                                                                            Linking agent**                                                                       AB ×                                                                         Product ×                                                                     Arms.sup.2                                  Ex. No.                                                                            Type mmol Type                                                                              mmol                                                                              10.sup.-3                                                                          10.sup.-3                                                                           per Star                                    __________________________________________________________________________    15   SSDCL                                                                              2.00 DVB 12  517  1,384 3                                           16   SSCL 4.00 DVB 24  117  857   7                                           17   SSDCL                                                                              2.87 DVB 17.2                                                                              239  1,261 5                                           18   αMSSCL                                                                       2.00 DVB 12  195  1,226 6                                           19   mSSCL                                                                              3.10 DVB 27.9                                                                              277  1,553 6                                           20   mSSCL                                                                              3.10 DEPO                                                                              0.221                                                                             209  436   2                                           21   mSSCL                                                                              2.60 PB  1.30                                                                              142  307   2                                           22   SSBr 1.875                                                                              DBE 0.94                                                                              138  322   2                                           23   SSTCL                                                                              0.83 --  --  570  570   --                                          __________________________________________________________________________     *SSCL = 4(chlorodimethylsilyl)styrene                                         SSDCL = 4(dichloromethylsilyl)styrene                                         αMSSCL = 4(chlorodimethylsilyl)-methylstyrene                           mSSCL = 3(chlorodimethylsilyl)styrene                                         SSBr = 4(bromodimethylsilyl)styrene                                           SSTCL = 4(trichlorosilyl)styrene                                              **DEPO = 1,2,7,8diepoxyoctane                                                 PB = phenylbenzoate                                                           DVB = divinylbenzene                                                          DBE = 1,2dibromoethane                                                        .sup.1 Weight average molecular weight: polystyrene equivalent as             determined by size exclusion gel permeation chromatography                    .sup.2 Ratio of MW (product) to MW (AB)                                  

EXAMPLE 24

This example demonstrates the preparation of block copolymer which israndomly-branched in both the vinyl aromatic and diene phases:

    br/2 - S.sub.20M -br/2 -1,4 - I.sub.120M

Following the procedure for Example 1, a randomly-branched styrenepolymer was produced from 2.0 kg cyclohexane, 6.0 mmol sec-butyllithium, 60.0 g styrene, and 3.0 mmol 4-(chlorodimethylsilyl)styrenecondensing agent. To the living polymeric anion obtained in this stepwas added (following the procedure set forth in Example 3) a 50%solution of 180.0 g isoprene in cyclohexane, to which 1.5 mmol4-(chlorodimethylsilyl)styrene had been added. After stirring for 3hours at 55°-60° C., the polymerization was terminated and the polymercooled, stabilized, and collected as described above. The weight averagemolecular weight of the product was 290,000, with a dispersity of 1.16(styrene equivalents).

Example 25

This example compares the melt viscosity characteristics of condensedphase block copolymers over a broad range of shear rates withstate-of-the-art linear triblock polymer, Kraton® 1107 (Shell Oil Co.),MW =175,000 (based on a 3M determination). Three different types ofcondensed phase block polymer are compared. The data are shown inFIG. 1. The melt viscosity was determined using a Siegloff-McKelveycapillary viscometer at 170° C., L/D =51. The melt viscosity for thepolymer of Example 3, shown as line B, which has incorporated abifunctional condensing reagent, was found to be an order of magnitudelower than the linear control sample, Kraton® 1107, shown as line D. Thepolymer of Example 4, which incorporates a trifunctional condensingreagent in the copolymerization of the isoprene segment has a meltviscosity (shown as line C) only slightly higher than the control, eventhough the molecular weight of the condensed block polymer is about 2.5times greater. When the condensing reagent is copolymerized in thevinylaromatic segment a remarkable reduction in melt viscosity isobserved. The data show that for the polymer of Example 1, shown as lineA, the viscosity characteristics are substantially the same as for thecontrol polymer, even though Example 1 is a condensed phase star polymerwith a molecular weight of about 853,000 (about five times the control).The effect persists when both polymers are tackified with 100 phr (partsper hundred rubber) Plus® (Goodyear Tire and Rubber Co.) and their meltviscosities compared, as shown in FIG. 2. ("At" refers to the viscositydata for the tackified polymer of Example 1 and "Dt" refers to tackifiedKraton® 1107 block copolymer control.) In addition to having a very lowmelt viscosity for its molecular weight, the "condensed" styrene phasestar polymer also shows a low dependence of viscosity on shear rate.

EXAMPLE 26

This example illustrates the rheological effects of random branching inthe rubbery or diene phase of block polymers.

Condensing together growing diene polymer chains in a more or lessrandom fashion during an anionic polymerization leads to polymers withunusual rheological properties when compared to conventional, linearmaterials. Comparison of a linear triblock polymer, Kraton® 1107 (ShellChemical Company), with a condensed diene phase styrene-isoprene blockpolymer, S_(10M) -br/2-I_(120M) (Example 3), using steady shearviscosity measurements performed at 190° C. on a Rheometrics MechanicalSpectrometer showed that, for the experimental condensed block polymer,the steady shear viscosity has a relatively low value of 10² Pa.s whichis shear rate-independent over the range shown in FIG. 3. (In FIG. 3,"D" refers to the Kraton® 1107 block copolymer control and "B" refers tothe polymer of Example 3.) This effect would be an advantage in hot meltcoatings, since better control and uniformity could be achieved due tothe Newtonian-like behavior of the polymer.

EXAMPLES 27 and 28

This example demonstrates the properties of pressure-sensitive adhesivecompositions derived from point-branched and randomly-branched blockpolymers.

The novel polymers of this invention were formulated intopressure-sensitive adhesives (PSAs) by solution blending in toluene thebranched or "condensed phase" block polymer, a synthetic hydrocarbontackifier resin, and 3 phr (parts per hundred rubber) Irganox® 1076stabilizer. These adhesive compositions were knife-coated at a thicknessof 25 micrometers onto primed 38-micrometer polyethylene terephthalatefilm, were dried for 5 minutes at 60° C., and were then conditioned for24 hours at 21° C. and 50% relative humidity. Tape testing was carriedout according to the test methods previously described, and the resultsare detailed in Tables IV and V below. In addition, Table V("Randomly-Branched Block Polymer PSAs") includes data for analogouslinear (unbranched) diblock polymer PSA compositions as comparativeexamples. The data shows that a significant improvement in PSAproperties is observed when a "condensing" reagent is copolymerized toform a branched or "condensed" polymer structure.

EXAMPLE 27

                  TABLE IV                                                        ______________________________________                                        Example 27                                                                    Point-Branched Block Polymer PSAs                                             Polymer                                                                       (Previous                                                                            Tackifier       Peel        Shear.sup.2                                Ex. No.)                                                                             Tradename (phr) (N/100 mm)  (RT, Min.)                                 ______________________________________                                        15     Wingtack Plus ®.sup.1                                                                  80     107       5,000+                                                       100    120       5,000+                                                       120    131       5,000+                                   17     Wingtack Plus ®                                                                        80     107       4,503                                                        100    116       10,000+                                                      120    129       10,000+                                  18     Wingtack Plus ®                                                                        80      99       5,000+                                                       100    123       5,000+                                                       120    136       5,000+                                   ______________________________________                                         .sup.1 Available from Goodyear Tire & Rubber Company                          .sup.2 +indicates that test was terminated at this point.                

EXAMPLE 28

Excellent shear and peel adhesion characteristics are also obtained withrandomly-branched block polymers when formulated in PSAs, as shown below

                  TABLE V                                                         ______________________________________                                        Randomly-Branched Block Polymer PSAs                                          Polymer                                                                       (Previous                                                                             Tackifier           Peel     Shear.sup.3                              Ex. No.)                                                                              Tradename (phr)     (N/100 mm)                                                                             (RT, Min.)                               ______________________________________                                        1       Wingtack Plus ®.sup.1                                                                  80     99       7,100+                                                        100    127      7,100+                                                        120    151      7,100+                                           Escorez ® 5300.sup.2                                                                   80     109      7,100+                                                        100    134      7,100+                                                        120    151      7,100+                                   3       Wingtack Plus ®                                                                        80     103      3,792                                                         100    142      4,000+                                                        120    166      3,847                                            Escorez ® 5300                                                                         80     109      4,100+                                                        100    120      4,100+                                                        120    74       4,100+                                   4       Wingtack Plus ®                                                                        80     120      10,000+                                                       100    116      10,000+                                                       120    120      10,000+                                  5       Wingtack Plus ®                                                                        80     88       5,000+                                                        100    99       5,000+                                                        120    114      5,000+                                   6       Wingtack Plus ®                                                                        80     99       6,000+                                                        100    118      6,000+                                                        120    112      6,000+                                           Escorez ® 5300                                                                         80     107      6,000+                                                        100    118      6,000+                                                        120    120      6,000+                                   7       Wingtack Plus ®                                                                        80     63       7,500+                                                        100    96       7,500+                                                        120    147      7,500+                                   8       Wingtack Plus ®                                                                        80     125      2,594                                                         100    151      1,498                                                         120    199(coh).sup.4                                                                         753                                      S.sub.10M -I.sub. 60M                                                                 Wingtack Plus ®                                                                        100    127      3                                        S.sub.10M -I.sub. 180M                                                                Wingtack Plus ®                                                                        100    116      8                                        ______________________________________                                         .sup.1 Available from Goodyear Tire and Rubber Company                        .sup.2 Available from Exxon Chemical Company                                  .sup.3 + indicates that test was terminated at this point                     .sup.4 (coh) indicates cohesive failure                                  

EXAMPLE 29

Pressure-sensitive adhesives formulated as in Example 28 have improvedhigh temperature shear performance compared to their linearcounterparts. As shown in Table VI, shear adhesion dramatically improvesas the condensing reagent is copolymerized in the isoprene phase. Thereis also a significant improvement in shear adhesion when the polymersare further linked with divinylbenzene to form a condensed phase starpolymer.

                  TABLE VI                                                        ______________________________________                                        Shear Adhesion at 66° C.                                               For PSA Formulations.sup.2                                                                                 Melt                                                          Time to failure.sup.1                                                                         Viscosity                                                     at load         (Pa.s × 10.sup.=2)                                      (minutes        (at 100 sec.sup.-1                               Polymer      at 66° C.)                                                                             shear rate)                                      Structure Ex.    200 g    500 g                                                                              1000 g                                                                              170° C.                                                                      190° C.                     ______________________________________                                        S.sub.10M --I.sub.120M                                                                  --     2        <1   <1    2.35  0.98                               S.sub.10M --br/                                                                         3      1184     20   3           1.8                                2-I.sub.120M                                                                  (S.sub.10M --I.sub.120M)                                                                --     >10,000  1478 59    7.7   6.5                                DVB                                                                           (S.sub.10M --br/                                                                        6      >10,000  4080 350   4.2   2.0                                2-I.sub.120M)                                                                 DVB                                                                           S.sub.10M --I.sub.180M                                                                  --     1712     13   >1    2.85                                     S.sub.10M --br/                                                                         4      3267     545  108   3.2   2.5                                3-I.sub.184M                                                                  S.sub.11.5M --I.sub.145M --                                                             Con-   2068     279  48    2.85  2.7                                S.sub.11.5M                                                                             trol.sup.3                                                          ______________________________________                                         .sup.1 Shear adhesion failure, 12.7 mm × 12.7 mm overlap,               25micrometer coat thickness on polyethylene terephthalate, all failures       were cohesive.                                                                .sup.2 Tackified with 100 phr Wingtack Plus.sup.                              .sup.3 Commercially available Kraton.sup. ® 1107 block copolymer     

EXAMPLE 30

This example illustrates the tensile properties of condensed-phasediblock polymers of the invention. Polymer films were prepared bycasting solutions of the polymer in toluene (30% solids) ontopolytetrafluoroethylene (Teflon®) sheets or silicone release linersusing glass cylinders as spacers. Solvent was allowed to evaporate overa period of 7 days. The sample was further dried in a vacuum oven at 40°C. for 48 hours. Stress-strain measurements were made using amodification of ASTM D 412 with a micro-dumbbell and 2 in./min.crosshead speed. An Instron Universal Testing Machine was used tomeasure the stress-strain properties of the samples. Elongation wasestimated by measuring the distance between bench marks on the sample.The stress was recorded continuously on a chart recorder.

                  TABLE VII                                                       ______________________________________                                        Tensile Properties of Condensed-Phase                                         Diblock Polymers                                                              Example    300% Modulus                                                                              Tensile    Elongation                                  Number     (psi)       Modulus (psi)                                                                            (%)                                         ______________________________________                                        3          75          390        1100                                        10         131         335        1025                                        11         150         594        1250                                        24         200         1000       1200                                        Kraton ® 1107*                                                                       112         2724       1300                                        ______________________________________                                         *Kraton ® 1107 is a linear styreneisoprene triblock polymer from Shel     Oil Co.                                                                  

While the invention has been described in terms of specific embodiments,it should be understood that it is capable of further modifications. Theclaims herein are intended to cover those variations which one skilledin the art would recognize as the chemical equivalent of what has beendescribed here.

We claim:
 1. A mormally tacky pressure-sensitive adhesive compositioncomprising:(a) an elastomeric anionic copolymer comprising thecopolymerized reaction product of(1) hydrocarbyl lithium initiator; (2)at least one anionically polymerizable monomer; and (3) a condensingagent monomer having the general formula

    CH.sub.2 ═C(R')QY(R).sub.n (X).sub.m

wherein Y is tetravalent Si, Ge, Sn, or Pb; X is H, --OR", CI, Br or F,wherein R" is a monovalent lower alkyl group having from 1 to 6 carbonatoms; R is hydrogen, a monovalent lower alkyl group having from 1 to 6carbon atoms, or phenyl; Q is phenylene; ' is hydrogen, a monovalentlower alkyl group having from 1 to 6 carbon atoms, or phenyl; m is aninteger of 1,2 or 3; and n is an integer equal to 3-m; and wherein themole ratio of (1) to (3) is about (1+m):1 and wherein the molepercentage of condensing agent in each copolymer segment containing saidcondensing agent is in the range of about 0.01% to about 5%; and (b)sufficient compatible tackifier to endow the composition with adhesivetack.
 2. The normally tacky pressure-sensitive adhesive composition ofclaim 1 wherein said anionically polymerizable monomer is selected fromthe group consisting of vinyl aromatic monomer and conjugated dienemonomer.
 3. The normally tacky pressure-sensitive adhesive compositionof claim 2 wherein said vinyl aromatic monomer is selected from thegroup consisting of styrene, alpha-methylstyrene, para-methylstyrene andt-butylstyrene.
 4. The normally tacky pressure-sensitive adhesivecomposition of claim 2 wherein said conjugated diene monomer is selectedfrom the group consisting of butadiene, isoprene, and piperylene.
 5. Thenormally tacky pressure-sensitive adhesive composition of claim 1wherein the mole percentage of said condensing agent in each copolymersegment cotaining condensing agent is in the range of about 0.02% toabout 2%.
 6. The normally tacky pressure-sensitive adhesive compositionof claim 1 wherein said condensing agent has the general formula

    CH.sub.2 ═C(H)QSi(CH.sub.3).sub.n (X).sub.m

where X is F, Cl, Br or methoxy.
 7. A normally tacky pressure-sensitiveadhesive composition comprising:(a) an elastomeric copolymer representedby the formula

    (B/Z).sub.y

where: B/Z is an elastomeric copolymer of conjugated diene compound anda condensing reagent having the general formula

    CH.sub.2 ═C(R')QY(R).sub.n (X).sub.m

where: X is H, --OR", Cl, Br or F wherein R" is a monovalent lower alkylgroup having from 1 to 6 carbon atoms; R is hydrogen or a monovalentlower alkyl group having from 1 to 6 carbon atoms or a phenyl; Y istetravalent Si, Ge, Sn or Pb; Q is phenylene; R' is hydrogen, amonovalent lower alkyl group having from 1 to 6 carbon atoms or phenyl;m is an integer of 1, 2 or 3; and n is an integer equal to 3-m; Y is aninteger from 1 to about 50; and wherein the mole percentage of Z in thesegment B/Z is in the range of about 0.01% to about 1%; and (b)sufficient compatible tackifier to endow the composition with adhesivetack.
 8. An adhesive coated sheet material comprising a backing havingat least one major surface at least partially coated with thepressure-sensitive adhesive composition of claim
 7. 9. The normallytacky pressure-sensitive adhesive composition of claim 7 wherein saidelastomeric copolymer is based upon a conjugated diene compound selectedfrom the group consisting of butadiene, isoprene, and piperylene. 10.The normally tacky pressure-sensitive adhesive composition of claim 7wherein said mole percentage of Z in the segment B/Z is in the range ofabout 0.02% to about 0.2%.